Apparatus for forming and dewatering a fibrous web

ABSTRACT

APPARATUS FOR FORMING AND DEWATERING A FIBROUS WEB COMPRISES, ACCORDING TO THE EXEMPLARY EMBODIMENTS, A FORMING ROLL AND A SUCTION COUCH ROLL SPACED AT SUBSTANTIAL DISTANCE FROM EACH OTHER GENERALLY HORIZONTALLY AND A FIRST MOVABLE, ENDLESS, TENSIONED FORAMINOUS BELT TRAINED AROUND A PORTION OF THE FORMING ROLL AND CONDUCTED ALONG A STRAIGHT RUN TO AND AROUND THE SUCTION COUCH. A SECOND BELT IS LED AROUND THE FORMING ROLL AND DEFINES WITH THE FIRST BELT AN ARCUATE WEB-FORMING ZONE EXTENDING ALONG A PORTION OF THE FORMING ROLL. THE TWO BELTS ARE LED IN CONVERGENT DIRECTIONS TO THE FORMING ROLL TO DEFINE A TAPERED INLET ZONE WHERE A RIBBON-LIKE JET OF FIBER STOCK IS INTRODUCED. THE TWO BELTS RUN TANGENTIALLY FROM THE FORMING ROLL TOGETHER ALONG A PART OF THE STRAIGHT PATH FROM THE FORMING ROLL TO THE COUCH ROLL, AND THE SECOND BELT IS SEPARATED FROM THE WEB PART WAY ALONG THE STRAIGHT RUN BY LEADING IT OUT AROUND A CARRIER ROLL. ONE OR MORE PRES-   SURE OR VACUUM BOXES ARE PROVIDED ALONG THE STRAIGHT RUN OF THE BELTS BETWEEN THE FORMING ROLL AND THE COUCH ROLL TO ESTABLISH A DIFFERENTIAL PRESSURE ACROSS THE WEB TO DEWATER IT. THE FIRST BELT, I.E., THE BELT WHICH RUNS FROM THE FORMING ROLL TO THE COUCH ROLL, IS ARRANGED SO THAT IT CARRIES THE WEB ON ITS UPPER SURFACE AFTER THE SECOND BELT IS SEPARATED. PRESS ROLLS MAY BE PROVIDED ALONG THE STRAIGHT RUN OR AT THE COUCH.

Feb. 23, 1971 JORDANSSQN I 3,565,757

v APPARATUS FOR FORMING AND DEWATERING A FIBROUS WEB Filed NOV. 27, 1968 INVENTOR. LARS BENGT JORDANSSON ATTORNEYS United States Patent M 3,565,757 APPARATUS FOR FORMING AND DEWATERING A FIBROUS WEB Lars Bengt Jordansson, Karlstad, Sweden, assignor to Aktiebolaget Karlstads Mekaniska Werkstad, Karlstad, Sweden, a company of Sweden Filed Nov. 27, 1968, Ser. No. 779,431 Claims priority, application Sweden, Nov. 28, 1967, 16,289/ 67 Int. Cl. D21f 1/48 U.S. Cl. 162 --301 7 Claims ABSTRACT OF THE DISCLOSURE Apparatus for forming and dewatering a fibrous web comprises, according to the exemplary embodiments, a forming roll and a suction couch roll spaced at substantial distance from each other generally horizontally and a first movable, endless, tensioned foraminous belt trained around a portion of the forming roll and conducted along a straight run to and around the suction couch. A second belt is led around the forming roll and defines with the first belt an arcuate web-forming zone extending along a portion of the forming roll. The two belts are led in convergent directions to .the forming roll to define a tapered inlet zone where a ribbon-like jet of fiber stock is introduced. The two belts run tangentially from the forming roll together along a part of the staright path from the forming roll to the couch roll, and the second belt is separated from the web part way along the straight run by leading it out around a carrier roll. One or more pressure or vacuum boxes are provided along the straight run of the belts between the forming roll and the couch roll to establish a differential pressure across the web to de- Water it. The first belt, i.e., the belt which runs from the forming roll to the couch roll, is arranged so that it carries the web on its upper surface after the second belt is separated. Press rolls may be provided along the straight run or at the couch.

BACKGROUND OF THE INVENTION This invention relates to apparatus for forming and dewatering a fibrous web, such as a paper or paperboard web.

For many decades, paper and paperboard have been produced, almost universally, on Fourdrinier machines in which a stock is spread across a moving foraminous belt, usually a metallic wire, and is drained along a run of wire of rather substantial length. Various improvements have been made over the years in the basic Fourdrinier machine. However, there are definite limits on the forming speed, principally because of the limited stock drainage rate that can be obtained.

In recent years, there has been a great deal of experimental and developmental Work on a markedly different type of paper-forming device, one in which stock is introduced as a high velocity, ribbon-like jet into a curved space, the outer portion of which is formed by a moving foraminous belt stretched around a curved member, such as a forming roll or a fixed, curved surface. The stock is drained by a combination of centrifugal forces resulting from the movement of the stock over a curved trajectory and the pressure of the tensioned belt, which squeezes the stock in the forming space. Experience with machines of this type has demonstrated that significantly hi her speed can be obtained With equipment which is of generally smaller size, lower cost and free of many of the problems of Fourdrinier machines.

Various specific machines of this type, which might be termed the pressure-forming type, have been proposed.

Patented Feb. 23, 1971 In many of them, the newly formed web is removed from the forming region in a manner which takes it into a reverse curve, relative to the original curvature along which it was formed. The movement of the web into a reverse curve before it reaches a relatively high dryness results in displacement and shear of the fibrous material, by virtue of the change in curvature of the respective surfaces of the Web, and has adverse effects on the strength, uniformity and other properties of the Web. In addition, the dryness of the web When it leaves the forming part is relatively low, and reliance is placed upon conventional presses down line from the forming equipment to further dewater the web prior to final drying. Often, the web is carried from the forming zone to the presses on the underside of a felt or wire running inside of the main, tensioned foraminous belt. This creates a high risk of breaks due to separation of the web from the under surface of such felt or wire.

SUMMARY OF THE INVENTION There is provided, in accordance with the present invention, a novel and improved apparatus for forming and dewatering a fibrous web which overcomes the above and other problems of pressure-forming type machines proposed heretofore. More particularly, the apparatus, according to the invention, comprises a first rotatable roll, a second rotatable roll spaced a substantial distance gen erally horizontally from the first roll and, of course, disposed parallel to the first roll and a first movable, endless, tensioned foraminous belt trained around portions of the first and second rolls and running in a straight run between them. A second foraminous endless belt runs generally conjointly with the first belt around the first roll, although it approaches the first roll in a convergent direction, relative to the first belt, so as to define a convergent inlet space where stock in the form of a ribbon-like jet is fed to the forming zone constituted by the region of the first roll where the two belts run together. The second belt moves conjointly with the first belt along a part of the straight run from the first roll to the second roll and is then trained around a guide roll and separated from the first belt leaving the web on the upper surface of the first belt.

The stock is dewatered in the forming zone and is formed into a web by combination of centrifugal force, which drives water out of the stock and out through the outer foraminous belt where it is collected and appropriately recovered, and by the pressure of the outer belt against the stock resulting from the tension of the outer belt. Further dewatering is accomplished along the straight run from the forming roll to the second roll by one or more pressure or suction boxes disposed along the straight run and creating a differential pressure across the web. The first and second rolls are arranged, relative to the two belts, so that the first belt runs to the couch roll with the web carried on its upper surface, thereby eliminating the problem of possible dropoif and breaks that can occur when the web is carried on the undersurface. Preferably, the Web is then taken off the first belt somewhere along a free run after it turns around the second roll and prior to the next carrier roll around which it is trained.

In addition to the basic advantage of employing the pressure-forming technique in the initial formation of the web, the apparatus of the invention offers the further advantages, as mentioned above, of providing a straight run of the web along a relatively substantial distance and of further dewatering of the web along the straight run. Consequently, the web leaves the forming and dewatering apparatus with a relatively high dryness, and is not subjected to turning until it reaches a relatively high dryness; thus, the possibilities of disruption of uniformity and impairment of the strength of the web are materially reduced. The geometric layout of the apparatus may be such as to make it possible to modify an existing Fourdrinier machine, to save many of the rolls and other parts of the machine, and to thereby provide a high speed, effective pressure-forming type machine at a relatively low cost.

DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be made to the following description of exemplary embodiments, taken in conjunction with the figures of the accompanying drawing, in which FIG. 1 is a side view in section taken just inside the near side frame of one embodiment, the drawing being of generally schematic form; and

FIG. 2 is a schematic side view in section taken just inside the near frame of another embodiment of the machine of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS The embodiment of FIG. 1 comprises a first rotatable roll 10, which may be termed a forming roll and preferably has a solid cylindrical surface. Spaced at a relatively substantial distance from the forming roll is a second rotatable roll 12, which is preferably a suction couch roll. An endless formaminous belt 14, which may be a wire or synthetic mesh or a paper-making felt, is trained around a portion of the surface of the forming roll 10, say on the order of 180 of the surface. The belt 14 then leads along a straight run around a portion of a couch roll 12 and returns to the forming roll over a series of guide or carrier rolls 16, 18 and 20 and a tension roll 22. The tension roll is of the type which provides a constant tension in the belt 14, such types of rolls being well known to those skilled in the art and therefore not being described or shown in detail. The rolls and belt are driven at uniform speeds so that they move conjointly.

A second movable, endless foraminous belt 24, preferably a paper making wire, is trained around the forming roll 10 in a manner such that it runs conjointly with the first belt 14 for the major portion of the zone where the first belt runs over the forming roll. The second belt is led to the forming roll 10 so that it converges toward the first belt 14 to define a stock inlet zone 26, and runs from the roll 10 conjointly with the first belt 14 over a part of the straight run between the forming roll 10 and the couch roll 12. At an appropriate point along the straight run the second belt 24 is separated from the first belt 14 by guiding it around a guide roll 28, and it then returns to the inlet part of the forming roll around guide rolls and 32, a tension roll 34 and a guide roll 36.

The arcuate region on the forming cylinder 10* where the two belts 14 and 24 run together constitutes a Webforming zone and is designated generally by the reference numeral 38. Stock is introduced from a nozzle 39 in the form of a ribbon-like jet traveling at a velocity of the same order of magnitude as the speed of the belts 14 and 24 into the converging inlet space 26 and forces its way into the forming space 38 where it is dewatered by a combination of centrifugal force resulting from the movement of the stock with the moving belts 14 and 24 around an arc and the pressure exerted by the tension of the outer belt 24 pulled over the are. The water thrown off and expressed outwardly from the stock as it is formed into a web in the forming zone 38 is collected in a collector box 40 and is recovered from an outlet 42.

The arcuate forming zone provides very rapid and efiicient removal of water from the web so that it leaves the forming zone with a relatively high dryness. However, the web is further dewatered along the straight run between the forming roll 10 and the couch roll 12 by a series of pressure or vacuum boxes. More particularly, the embodiment of FIG. 1 shows a series of suction boxes '44 arranged adjacent each other below the upstream portion of a straight run of the belts 14 and 24 for creating by a vacuum a differential pressure across the web. It will be understood that the suction boxes 44 may be replaced by a single box, or that one or more pressure boxes may be utilized in place of the suction boxes. Preferably, however, the differential pressure created across the web during the initial dewatering phase along the straight run between the forming roll 10 and the couch roll 12 is maintained substantially continuously. In the region where the first belt 24 is separated from the second belt 14 (namely at the roll 28), the suction is kept on to hold the web on the first belt.

Desirably, additional suction boxes are located downstream along the run of the belt 14 between the roll 28 and the couch roll 12 where the web is carried on its upper surface. For example, the embodiment of FIG. 1 includes two adjacent suction boxes 46 along this part of the straight run of the belt 14. The dewatering apparatus along the straight run may also include a press roll 48, which is backed up by one of the suction boxes 46, and, finally, the forming and dewatering apparatus may be assisted by another press roll 50 backed up by the suction couch roll 12, When the web reaches the suction couch, it will have a relatively high dryness so that it may be turned through an S curve without impairing its quality or strength and may be removed in an open draw by turning it around and picking it off with a suction pick up roll 52. Advantageously, the Web is removed from the belt 14 along a free run between the couch roll and the carrier roll 16.

The embodiment of FIG. 2 is quite similar to the embodiment of FIG. 1 except for the particular geometry and arrangement of the forming roll and the two foraminous belts. It comprises a forming roll 100, again preferably of an appropriate construction providing a solid cylindrical surface, a suction couch roll 102 and an endless, tensioned foraminous belt 104 corresponding to the first belt :14 of the embodiment of FIG. 1. The principal diflierence between the two embodiments is that the belt 104 constitutes the outer belt around the forming cylinder 100, thus serving as the primary tensioned forming element. The belt 104 is conducted around guide rolls 106 and 108, a tension roll 110 and guide rolls 112, 114, 116 and 118 and back to the forming roll 100.

A second endless foraminous belt 120 approaches the forming roll 100 along a path convergent to the first belt 104, thereby providing a stock inlet zone 122 for the introduction of stock in the form of ribbon-like jet from a nozzle 124, and then turns substantially conjointly with the first or outer belt 104 around the forming roll to define an arcuate web forming zone 126. The two belts 104 and 120 travel together along a portion of a straight run of the belt 104 between the forming roll 100 and a couch roll 102 to a point where the second or inner belt 120 is separated by turning it around a guide roll 128. The inner belt 120 is guided around a constant tension roll and a guide roll 132 back to the forming roll 100.

As in the embodiment of FIG. 1, the jet of stock introduced at the inlet zone 122 defined between the belts 104 and 120 where they converge toward the forming roll 100 is dewatered by a combination of centrifugal forces and the pressure established by the tension in the outer belt 104, the water thrown off and expressed from the web being captured and recovered by a collector box 134. The web is then carried in between the two belts 104 and 120 along a series of suction boxes 136 and 138 which may be disposed substantially as in the embodiment of FIG. 1. The embodiment of FIG. 2 omits a pressure roll along the straight run of the belt '104, but includes a pressure roll 140 backed up by the suction couch roll 102. The web is separated in the same manner as in the embodiment of FIG. 1 by a suction pickup roll 1'42.

I claim:

1. Apparatus for forming and dewatering a fibrous web comprising a first rotatable roll, a second rotatable roll spaced a substantial distance generally horizontally from the first roll and disposed parallel to the first roll, a first movable endless tensioned foraminous belt trained around portions of the first and second rolls and extending tangentially to the first and second rolls and along a straight run between them, a third roll closely adjacent the straight run portion of the first belt, a second movable endless tensioned foraminous belt trained around a part of the first roll, such part including a zone in which the first and second belts run together to define an armate web-forming zone, and the two belts leading to the first roll along convergent paths, defining a stock inlet zone and leading from the first roll together and traveling together along a part of the straight run of the first belt with the second belt overlying the first belt, and the second belt being trained around the third roll and being led away from the first belt so that the first belt continues alone along the remainder of the straight run to the second roll, means for introducing stock in the form of a ribbon-like free jet into the stock inlet zone, whereby a web is formed between the two belts in the web-forming zone and is carried with the belts, first dewatering means disposed along the part of the straight run of the belts between the first and third rolls to create a pressure difierential across the fibrous web to dewater the web, second dewatering means disposed along the part of the straight run between the third and second rolls to create a pressure differential across the first belt and the fibrous web to further dewater the web, and means for separating the fibrous web from the first belt after they pass over the second roll.

2. Apparatus according to claim 1 wherein the second roll is a suction couch.

3. Apparatus according to claim 1 wherein the first belt is tangent to the first and second rolls at an upper point thereon, and wherein the first belt runs inside the second belt around the first roll.

4. Apparatus according to claim 1 wherein the first belt is tangent to the first roll at a lower point thereon and is tangent to the second roll at an upper point thereon, and wherein the second belt runs inside the first belt around the first roll.

5. Apparatus according to claim 1 wherein the second dewatering means for creating a pressure difierential includes a suction box and a press roll between the second and third rolls engaging the web and first belt against the suction box.

6. Apparatus according to claim 2 wherein the second dewaterin g means for creating a pressure differential comprises a press roll engaging the web and first belt against the suction couch roll.

7. Apparatus according to claim 1 wherein the first dewatering means for creating a pressure differential includes a suction box in the portion of the straight run between the first and third rolls, said suction box also extending beyond the third roll to ensure that the web is retained on the first belt.

References Cited UNITED STATES PATENTS 3,224,928 12/1965 Lee et al. 162317X 3,400,045 9/1968 Graham 1 62-317 3,438,854 4/1969 Means 162-203X S. LEON BASHORE, Primary Examiner A. L. CORBIN, Assistant Examiner US. Cl. X.R.

@ 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 r r Dated Feb. 23 1971 lnvent fl L. B. Jordansson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 28, 7 Column 1, line 68, "speed" should be -speeds-- line 31, delete "the first belt and".

"staright should be --straight-- Column 5,

Signed and sealed this 31 at day of August 1971 (SEAL) Attest:

EDWARD M.FLEICHER, JR. Attesting Officer WILLIAM E. SCHUYLER, JR. Commissioner of Patents 

